The present invention concerns electromagnetic compatibility measurements and pertains particularly to automatic adjustment of cables which aids in set-up of equipment under test for electromagnetic compatibility measurements.
In order to comply with various regulations and to satisfy performance requirements of consumer, electronic equipment are required to conduct and radiate less than a maximum limit of unwanted electromagnetic energy and are required to have a certain level of immunity against other electromagnetic sources. Measurement methods are supplied in standards such as IEC 1000-4-3, IEC 1000-4-6, ANSI C63.4, CISPR 22.
The coupling of energy to and from a system is not only influenced by the design of the system but also by the set-up of the system, as particularly as pertains to distances between a ground plane and various subparts of the system. The routing of cables also can have a significant impact on the coupling of energy.
For example, ANSI C63.4 in 6.2.1.3 and CISPR 22 in 9.1, and the relating regulation of the European Community require cable maximization in emissions measurement. For example CISPR requires that "An attempt shall be made to maximize the disturbance consistent with the typical applications by varying the configuration of the test sample . . . The effects of varying the position of the cables shall be investigated to find the configuration that produces maximum disturbances."
Not only emissions measurement results, but also immunity measurement results strongly depend upon cable routing and equipment under test (EUT) setup.
In the past, the cable and set up influence has often been completely ignored. However, now if the cable and set up influence are ignored the result may be that requirements required by law may not be fulfilled resulting in a risk of high fines, shipment halts, expensive retesting, expensive changes to products and market release, and/or loss of reputation.
In some cases the cable and setup influence is not investigated on each test but the possible influence of the cable and setup are taken into account by reducing the acceptable limits in emission testing and by increasing the test level during immunity testing. However, the influence of cable routing and test setup may vary by a large amount even in response to subtle changes in position. To avoid shipping electronic systems which do not fulfill the legal or customer requirements, a significant reduction in the emission level and a significant increase in the immunity level may required when the possible influence of the cable and setup are taken into account in this way.
Further, when cable and setup influence is not investigated on each test but the possible influence of the cable and setup are taken into account by reducing the acceptable limits in emission testing and by increasing the test level during immunity testing, this can result in the necessity of investment of additional material and design effort to comply with the reduced limit in emission testing and to deal with the increased test level in immunity testing. This additional material and design effort is unnecessary when exact knowledge on cable and setup influence is obtained.
Also, to attempt to obtain exact knowledge on cable and setup influence, the influence of cable routing and setup can be investigated by hand with test interruption. To do this, the test area is entered and the cable routing and/or the setup is changed. However, to avoid potentially hazardous fields, during immunity testing, the generation of testing signals needs to be halted when performing immunity testing. While testing for emission levels of equipment under test, it is generally not necessary for an operator to turn off the test equipment before entering the testing area. Additionally, because of potential influence on testing levels for both immunity testing and emissions testing, it is generally advisable that an operator leave the test area while testing is actually being performed. Such a testing process can be very time consuming when a number of different cable and setup positions are tested.
To reduce the time of testing, during emissions testing, the operator can remain within the testing area to allow for quicker adjustment of the setup and cables. Because of the potentially hazardous fields, however, it is generally not advisable for an operator to be present during immunity testing. Additionally, the presence of personal within the testing area can have a detrimental impact on testing. It may then be necessary to take this into account by reducing the acceptable limits in emission testing. In any event the manipulations required even when the operator are present are still very time consuming.